Make sure to also check your tapes. Open the flap and make sure the tape doesnt have wrinkles, waves, or tears. Usually near the end of the tape is where you will want to check the tape physically. Dirty and damages tapes can effect the drum and of course dirty the heads. A tape cleaner is fine, it will get the surface and work a bit longer, but professional service every couple hundred hours is the way to go because full adjustments can be made to the unit as well.
http://www.tekmg.com